In a piston-type internal combustion engine having mechanically actuated cylinder valves that are actuated with the aid of at least one camshaft via roller drag levers, it is possible to deactivate the cylinder valves of a portion of the cylinders in order to operate the engine in partial-load operation, for example, operations which only some of the cylinders are fired, whereas the cylinders having deactivated cylinder valves are not fired, but are idle. The cylinder valves can be deactivated cyclically, so other cylinders can always be fired, taking into consideration running smoothness. The active cylinders can then be fired under full-load conditions, and thus under optimum operating conditions, with the piston-type internal-combustion engine only delivering a partial load overall.
The arrangements known to this point for deactivating the cylinder valves have a very complicated design, and require a considerable amount of space.
It is the object of the invention to provide a piston-type internal-combustion engine having deactivatable cylinder valves and a simple valve-gear design.
This object generally is achieved according to the invention with a piston-type internal-combustion engine having deactivatable, mechanically actuated cylinder valves that are respectively actuated by at least one camshaft via of a roller drag lever with a roller. The lever is configured from two partial levers that are hinged to one another via an articulated shaft, on which the roller associated with a cam of the camshaft is rotatably seated, and having a locking mechanism that can be switched to act between the two partial levers and is used to activate or deactivate the force transmission between the camshaft and the cylinder valve. The free end of the one partial lever is supported on the cylinder valve, and a support is provided on the engine block for the free end of the other partial lever. The engine further has a restoring spring that is effective between the two partial levers, and presses the roller along the cam when the partial levers are unlocked. The fact that the articulated shaft for the two partial levers simultaneously acts as a bearing for the roller greatly simplifies the design of the valve gear. The restoring spring ensures that, when the cylinder valve is deactivated, the two partial levers are guided with the roller along the cam contour, so the roller remains in contact with the cam in this operating mode. At the same time, it is ensured that, after the piston-cylinder unit has been set to zero pressure, the two partial levers assume their extended position for as long as the roller is in contact with the base circle of the cam, and the locking element can extend into its receptacle and lock the two partial elements together.
A particularly advantageous embodiment of the invention provides that the partial lever associated with the cylinder valve has an extension that faces the support and extends past the articulated shaft. The extension overlaps a region of the partial lever associated with the support in scissors fashion, and the latching mechanism is associated with the region in which the two partial levers overlap like scissors.
A further advantageous embodiment of the invention provides that the locking mechanism is formed by a piston-cylinder unit that can be supplied with compressed oil and is disposed in the partial lever associated with the support. The piston-cylinder unit further has a locking element that can be displaced parallel to the articulated shaft, and that has a piston portion and a bar portion. The bar portion and the piston portion can be formed as separate components or, in an advantageous embodiment of the invention, they can be connected to one another in one piece. It is practical to provide a restoring spring that holds the locking element in its latched position, so in normal operation, the two partial levers are locked together and are not unlocked until the piston-cylinder unit is supplied with compressed oil, and the corresponding cylinder valve is thus deactivated.
A further advantageous embodiment of the invention provides that the piston-cylinder unit is supplied with compressed oil via a hydraulic play-compensation element that forms the support. This type of hydraulic play-compensation element is present anyway in the arrangement of the roller drag levers, so in order to supply compressed oil to the piston-cylinder unit, it is only necessary to provide a corresponding compressed-oil conduit in the partial lever resting on the compensation element, the conduit being connected to the cylinder of the piston-cylinder unit. The spring force of the restoring spring of the piston-cylinder unit is selected such that the spring is not compressed at the pressure level required for the play compensation, and with the given piston surface, so the roller of the roller drag lever remains in constant contact with the cam. If a cylinder valve is to be deactivated, the pressure in the compressed-oil supply of the play-compensation elements is increased to the point that the restoring spring of the locking element compresses, thus releasing the lockup of the two partial levers. If the relevant cylinder valve is to be re-activated, the oil pressure is reduced correspondingly, so the restoring spring re-engages the locking element with the other partial lever, and locks the two partial levers together.
A still further advantageous further embodiment of the invention provides that at least the partial lever that is associated with the cylinder valve is formed in a claw or u-shaped jaw shape or u-shaped jaw, and extends laterally around the roller in the region of the articulated shaft, with one jaw part forming the extension. This embodiment offers a very stable, compact construction of the roller drag lever, which simultaneously permits the articulated shaft and the roller to be seated properly.